Dependence of the depth of the Earth ’ s plasma depletion layer on the interplanetary magnetic field direction and the Alfvénic Mach number

The Earth’s magnetosheath, the transition region between the Earth’s magnetopause and the bow shock, is a space laboratory for the investigation of magnetoactive plasmas. Analogeous studies are also the aim of the LAPLAS experiment planned for the FAIR facility at GSI [1]. One of the recent problems of the magnetosheath physics is the dependence of its plasma depletion layer on the direction of the interplanetary magnetic field. If the interplanetary magnetic field is directed southward, than, at the magnetopause, also hot ion beams may be excited by magnetic reconnection processes. Pudovkin et al. [2] developed a well-accepted isotropic 2D-MHD magnetosheath model considering magnetic reconnection at the dayside. Thereat they showed that reconnection changes the topology of the solar wind plasma flow. The predominating velocity in the plane perpendicular to the Sun-Earth line is perpendicular to the magnetic field ~ B at northward solar wind magnetic field (Θm < 57), and perpendicular to the reconnection line at southward solar wind magnetic field. Besides Pudovkin et al. substituted the generally considered condition of vanishing normal component of the solar wind velocity vn at the magnetopause by the new boundary condition vn = Mamp|sin(Θm − φ)|Bm/ √ 4πρm. Here Θm describes the angle between the direction of the solar wind magnetic field at the magnetopause and the direction which is perpendicular to the Sun-Earth line and lies in the plane containing this line and the Earth’s magnetic dipole axis. Mamp is the Alfvénic Mach number, and ρm is the mass density of the solar wind at the magnetopause. φ determines the orientation of the reconnection line [3]. In Fig. 1, new results of a detailed analysis of profiles of the magnetosheath mass density ρsh along the subsolar stream line from the bow shock (x = 1.0) to the Earth’s magnetopause (x = 0.0) are shown, which are found using the Pudovkin et al. model. The mass density is normalized by the solar wind mean mass density ρsw. It is to be seen that the depth of the plasma depletion layer is largest for southward interplanetary magnetic field (Θsw = 180) and becomes less pronounced with the increase of Masw. Masw is the Alfvénic Mach number of the solar wind in front of the bow shock. Besides the mass density decrease at the magnetopause is weaker if Mamp grows.